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Ivermectin: Superior Efficacy Against Mange Mites

by 5m Editor
25 March 2001, at 12:00am

By Prof. Dr. J. Vercruysse and Dr. K. Smets, University of Gent - The unique pharmacological characteristics of ivermectin, related to its potent systemic activity against Sarcoptes scabiei var suis, have been demonstrated worldwide; This report describes several mange efficacy trials performed with Ivomec, Merial's brand of ivermectin.

Ivomec Acts where Mange Mites and Lice Occur

Mite eggs
Mite eggs deposited in burrows in skin. Larvae that hatch may create side tunnels or leave the area and migrate to undamaged skin to burrow new tunnels.
When Ivomec is given subcutaneously at a dose rate of 300 µg/kg, high concentrations of ivermectin are found in the ear wax, skin, and ears. The great predilection for mites to concentrate in these sites makes Ivomec particularly useful against mites (Scott and McKellar, 1992).

Recent studies have confirmed the persistent activity of Ivomec Injection, with no mites recovered for 6 weeks after pigs were challenged 12 days post Ivomec treatment (Cargill et al, 1999). This finding suggests that Ivomec outlasts the mite egg incubation period, estimated to be 3 to 10 days. No difference was found between Ivomec and DECTOMAX® (doramectin) when pigs were challenged more than 12 days post treatment.

The eradication of mange from large pig herds on many farms in Denmark (Ebbesen and Henriksen, 1986; Jensen, 1988; Ebbesen, 1998), Holland (Lambers, 1994, Rambags et al, 1998), Belgium (Smets et al, 1998), Australia (Cargill et al, 1996), Germany (Koheler and Zabke, 1998), USA (Mohr, 1999), illustrates that in practice, the efficacy and prolonged protection induced by Ivomec Injection or Premix, effectively breaks the mange mite life cycle.

Study after study shows the high efficacy of Ivomec. Many studies provide evidence that Ivomec Injection at 300 µg/kg eliminates Sarcoptes scabiei from infested pigs (Lee et al, 1980; Brokken et al, 1983; Alva-Valdes et al, 1984). The recommended dose level of Ivomec Premix 100 µg/kg given for 7 consecutive days has also been shown to provide complete efficacy against internal and external parasites (Alva-Valdes et al, 1989; Foster et al, 1992; Wallace et al, 1996).

Ivomec: Trial Designs

In the design of efficacy trials against S. scabiei, the detection of mites is critical; a positive diagnosis is made when live mites are found in skin scrapings taken from deep inside the pinna of the ear. Because this technique has a low sensitivity (that is, scrapings will miss mites on many occasions) repeated sampling was completed to increase the chance of detecting mites. The main aim of treatment should be complete elimination of all mites in all animals, as a 100% cure rate will ensure eradication of mites from a herd. The reduction of clinical signs — erythematous papules, skin abrasions, hair loss, encrusted lesions, pruritus — may be a more sensitive indicator of efficacy, since a high percentage of animals show lesions before mites are detected. Other variables used to determine product efficacy, such as reductions in dermatitis score and antibody concentrations, need to be considered cautiously; they may be more useful when overall control and eradication programs are considered.

Studies Prove Consistent Efficacy of Ivomec against
Sarcoptes scabiei var suis

Several studies confirm the efficacy of Ivomec, in the absence of reinfection, based on the presence or absence of mites in ear scrapings before and up to 42 days after treatment. Tables 1 and 2 summarise studies performed with Ivomec Injection and Ivomec Premix. In six of the eight studies with Ivomec Injection, the cure rate was 100%. In the two remaining studies, overall mite reduction was >99%. The cure rate in the eight trials performed with Ivomec Premix was 100%.

Other independent authors have also reported excellent results. Courtney et al, 1983, showed that treatment of infected sows with Ivomec Injection 8 to 37 days before farrowing eliminated mange from the sows and prevented transmission to the piglets. Pigs farrowed by sows treated with Ivomec remained noninfected until the termination of the experiment at 12 weeks of age (White and Ryan, 1987; Dalton and Ryan, 1988; and Martineau et al, 1984). Similar results with Ivomec Premix were reported by Primm et al, 1992. Finally, Nilsson et al, 1994, Roppa et al, 1996, and Garcia et al, 1998, described effective control of sarcoptic mange in growing pigs under natural challenge in production-type conditions typical of Sweden, Brazil, and Canada, respectively. Cleaner carcasses, fewer days to achieve market weight, and improvement in feed efficiency were reported.

Table 1. Summary of sarcoptic mange efficacy studies in pigs
treated with Ivomec Injection
Trial No. of
Controls
Day Number
Medicated
Day
-1/0 14 28 42 -1/0 14 28 42
US1 8 71.5 59.3 209.7 43.6 4 70.9 0.0 0.0 0.0
GER1 3 7.4 11.9 11.4 0.6 2 3.7 0.0 0.0 0.0
US2 3 3.3 -- 0.6 7.6 6 12.0 -- 0.0 0.0
GER2* 5 7.2 2.2 0.0 0.0 5 6.8 0.3 0.0 0.0
US3 6 3.9 4.3 5.8 8.9 6 4.8 0.0 0.0 0.0
S Af 6 342.2 -- 335.8 280.7 12 241.2 -- 0.0 0.0

GER3 5 108.8 90.9 65.8 57.9 5 238.2 2.3 1.3 0.7

Overall** reduction
from control 46 27.6 14.1 18.4 15.0 50 114.5 0.3 0.1 0.1 >98% >99% >99% Reduction from
pretreatment >98% Data from Cramer et al (1996)
*Pigs were treated intramuscularly. Pigs were naturally infested in all studied except GER2.
**Trials equally weighed.
US = United States; GER = Germany; S Af = South Africa; AUS = Australia.

Table 2. Summary of sarcoptic mange efficacy studies in pigs
treated with Ivomec Premix
Trial No. of
Controls
Day Number
Medicated
Day
Pre 14 28 42 Pre 14 28 42
SP* 9 71.4 38.3 17.7 22.6 9 63.3 0.0 0.0 0.0
US1 8 54.1 73.2 31.9 18.4 8 35.3 0.0 0.1 0.0
US2* 28 6.2 9.0 4.7 1.3 27 6.0 0.0 0.0 0.0
US3* 10 18.8 4.7 2.5 0.1 10 15.5 0.0 0.0 0.0
US4* 10 1.0 1.0 0.4 0.1 10 1.4 0.0 0.0 0.0
GER* 10 37.7 9.1 >6.9 3.6 10 32.0 0.0 0.0 0.0

US5* 7 115.6 35.4 21.2 2.2 7 102.3 0.0 0.0 0.0 US6** 8 61.3 53.9 39.4 49.0 8 59.1 0.0 0.0 0.0 Overall** reduction
from control 26.84 15.9 9.2 4.6 81 23.6 0.0 <0.1 0.0 >100% >99% >100% Reduction from
pretreatment 100% Pigs were naturally infested in all studied except USA4 and GER (induced infestation superimposed on natural).
*Data from Cramer et al (1996)
**Data from Alva-Valdez.
SP= SPAIN; US = United States; GER = Germany.

The cure rate in the eight trials performed with Ivomec Premix was 100%.

Discussion

Results of reviewed trials confirm that Ivomec, administered subcutaneously as a single dose of 300 µg/kg or given in the feed during 7 consecutive days at a dose level of 100 µg/kg/day, is safe and highly effective against S. scabiei in pigs. Moreover, the extensive use of Ivomec as an endectocide for pigs has demonstrated its consistent and reliable parasite control to the swine industry for more than 15 years. Ivomec Premix may be the preferable formulation when treating large groups of swine.

Given the high efficacy of Ivomec, it is the product of choice for an eradication program in which all swine in the facility are given two strategic Ivomec treatments. Time intervals may vary, depending on locally approved withholding periods (Ebbesen and Henriksen, 1986; Jensen, 1988; Ebbesen, 1998; Lambers, 1994; Cargill et al, 1996; Rambags et al, 1998; Smets et al, 1998; Koehler and Zabke, 1998; Mohr, 1999). It is also the product of choice for an effective control program for a farrow-to-finish swine facility in which a single treatment to sows is administered just before they are moved into the farrowing house, and to grower pigs when moved to the grower/finisher phase around 8 to 12 weeks of age.

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